Familial influences on tests of mental and motor performance at ages eight months and four and seven years were examined by comparing correlation co-efficients among monozygotic twins, dizygotic twins, full siblings, half siblings, and cousins within race, sex, and social class groups. Similar correlations among physical measurements at these ages were also examined. A paper has been published on familial resemblance in infant mental development. The correlations between scores of twin and sibling pairs on the Stanford-Binet (age 4) and Wechsler (age 7) intelligence tests suggested a greater genetic influence than was found for infant test scores. This project is completed and a final paper is in preparation.